Field of the Invention
The invention relates to a lens. More particularly, the invention relates to a zoom lens.
Description of Related Art
Generally speaking, zoom lenses that are commonly available to the market are large-aperture and wide-angle zoom lenses. However, a wide-angle lens is not capable of clearly recognizing distant images and therefore, when being applied to long-distance security monitoring in locations, such as long corridors, long type shelves in shopping malls and so on, the large-aperture and wide-angle zoom lenses can not satisfy the demands of clearly recognizing distant images.
On the other hand, in a zoom lens, aspheric lenses are used to achieve a wide angle so as to mitigate image aberrations and chromatic aberrations. Aspheric lenses may achieve good effects of aberration correction; however, too much use of aspheric lens would result in dramatically cost rise.
Accordingly, how to achieve good image quality of the zoom lenses and the reduction of production cost has been a major subject of the development in the related field.
For instance, in U.S. Pat. Nos. 7,405,885, 7,061,687, 7,489,452 and 4,348,082 as well as U.S. publication Nos. 2010182677 and 2006034000, zoom lenses are disclosed.